Protein C, when activated to form activated protein C (APC), plays a major role in three biological processes or conditions: coagulation, fibrinolysis and inflammation. Acute inflammatory states decrease levels of the free form of protein S, which decreases APC function because free protein S is an important co-factor for APC. Sepsis, acute inflammation and cytokines decrease thrombomodulin expression on endothelial cells resulting in decreased APC activity or levels. Septic shock also increases circulating levels of thrombomodulin, which is related to increased cleavage of endothelial cell thrombomodulin. Another mechanism for decreased APC function in sepsis is that endotoxin and cytokines, such as TNF-α, down-regulate endothelial cell protein C receptor (EPCR) expression, thereby decreasing action of APC. Severe septic states such as meningococcemia, also result in protein C consumption. Depressed protein C levels correlate with purpura, digital infarction and death in meningococcemia.
Protein C is altered in non-septic patients following cardiopulmonary bypass (CPB). Total protein C, APC and protein S decrease during CPB. Following aortic unclamping (reperfusion at the end of CPB) protein C is further activated so that the proportion of remaining non-activated protein C is greatly decreased. A decrease of protein C during and after CPB increases the risk of thrombosis, disseminated intravascular coagulation (DIC), organ ischemia and inflammation intra- and post-operatively. Patients who have less activated protein C generally have impaired recovery of cardiac function, consistent with the idea that lower levels of protein C increase the risk of microvascular thrombosis and myocardial ischemia. Aprotinin is a competitive inhibitor of APC, and is sometimes used in cardiac surgery and CPB. Aprotinin has been implicated as a cause of post-operative thrombotic complications after deep hypothermic circulatory arrest.
Septic and non-septic stimuli such as bacterial endotoxin and cardiopulmonary bypass (CPB), activate the coagulation system and trigger a systemic inflammatory response syndrome (SIRS). A decrease in protein C levels have been shown in patients with septic shock (GRIFFIN J H. et al. (1982) Blood 60:261-264; TAYLOR F B. et al. (1987) J. Clin. Invest. 79:918-925; HESSELVIK J F. et al. (1991) Thromb. Haemost. 65:126-129; FIJNVANDRAAT K. et al. (1995) Thromb. Haemost. 73(1):15-20), with severe infection (HESSELVIK J F. et al. (1991) Thromb. Haemost. 65:126-129) and after major surgery (BLAMEY S L. et al. (1985) Thromb. Haemost. 54:622-625). It has been suggested that this decrease is caused by a decrease in protein C transcription (SPEK C A. et al. J. Biological Chemistry (1995) 270(41):24216-21 at 24221). It has also been demonstrated that endothelial pathways required for protein C activation are impaired in severe menigococcal sepsis (FAUST S N. et al. New Eng. J. Med. (2001) 345:408-416). Low protein C levels in sepsis patients are related to poor prognosis (YAN S B. and DHAINAUT J-F. Critical Care Medicine (2001) 29(7):S69-S74; FISHER C J. and YAN S B. Critical Care Medicine (2000) 28(9 Suppl):S49-S56; VERVLOET M G. et al. Semin Thromb Hemost. (1998) 24(1):33-44; LORENTE J A. et al. Chest (1993) 103(5):1536-42). Recombinant human activated protein C reduces mortality in patients having severe sepsis or septic shock (BERNARD G R. et al. New Eng. J. Med. (2001) 344:699-709). Thus protein C appears to play an important beneficial role in the systemic inflammatory response syndrome.
The human protein C gene maps to chromosome 2q13-q14 and extends over 11 kb. A representative Homo sapiens protein C gene sequence is listed in GenBank under accession number AF378903. Three single nucleotide polymorphisms (SNPs) have been identified in the 5′ untranslated promoter region of the protein C gene and are characterized as −1654 C/T, −1641 A/G and −1476 A/T (according to the numbering scheme of FOSTER D C. et al. Proc Natl Acad Sci USA (1985) 82(14):4673-4677), or as −153C/T, −140A/G and +26A/T respectively by (MILLAR D S. et al. Hum. Genet. (2000) 106:646-653 at 651).
The genotype homozygous for −1654 C/−1641 G/−1476 T has been associated with reduced rates of transcription of the protein C gene as compared to the −1654 T/−1641 A/ −1476 A homozygous genotype (SCOPES D. et al. Blood Coagul. Fibrinolysis (1995) 6(4):317-321). Patients homozygous for the −1654 C/−1641 G/−1476 T genotype show a decrease of 22% in plasma protein C levels and protein C activity levels as compared to patients homozygous for the −1654 T/−1641 A/−1476 A genotype (SPEK C A. et al. Arteriosclerosis, Thrombosis, and Vascular Biology (1995) 15:214-218). The −1654 C/−1641 G haplotype has been associated with lower protein C concentrations in both homozygotes and heterozygotes as compared to −1654 T/−1641 A (AIACH M. et al. Arterioscler Thromb Vasc Biol. (1999) 19(6):1573-1576).